This invention relates to apparatus for generating smoke having precisely controllable quantities and qualities, especially for use in the movie and entertainment industry. More particularly, it relates to a portable smoke-generating device having a vaporizing chamber with a very high surface area/volume ratio.
Liquid vaporizers of various types have been used for many years for many purposes. For example, spraying of fertilizers and insecticides by pumping a liquid through a fine nozzle under high pressure is common practice. The generation of smoke in airplane exhausts for skywriting purposes, and for fire simulations for firefighters' training, is also well known. Since precision of control of smoke-generating units is generally not an important design criterion, commercial smoke-generating units generally consist of relatively simple units having vaporizing chambers capable of rapidly heating a smoke generating liquid to above its flash point, and a nozzle for directing the smoke produced in the device to the desired location. A typical smoke-generating device of this type is shown in Swiatosz, U.S. Pat. No. 4,303,397. This patent i discloses a portable smoke generator having a centrifugal pump which pumps a liquid through a tubular coil in which the liquid is vaporized for discharge through a nozzle. While this device is suitable for the purpose for which it was designed, i.e., to simulate a fire for training a student how to handle a fire, it is not adequate to produce smoke of sufficient quality and with sufficient flexibility to produce special effects for the motion picture industry.
The entertainment industry, and particularly the television and motion picture film industry, has continuous requirements for smoke generation for a wide variety of purposes and effects. In addition to creating the most obvious special effects in a film (e.g., the generation of smoke to simulate a fire), smoke-generating machines are used to help create hundreds of different special effects when filming. Smoke machines can be used to create the effect of fog, clouds, chimney smoke, discotheque haze, and to obscure background elements which are not desirably seen on film. Artistic effects, such as light "shafting", are also created by smoke. For example, if filming is being carried out in a large building or in a church, a film director may desire a very slight haze in the building so that light coming in through a window or skylight will appear on the film in visible "shafts". To create this effect without creating an appearance of an actual haze or fog requires extremely precise control over the amount and quality of smoke exhausted into the building.
Indeed, the use of smoke in filming is more commonly for artistic purposes than for the creating of the appearance of actual smoke. On film, smoke creates the impression of depth of field, whereas a camera itself has no depth of field. When using smoke during filming, the smoke must be created instantly (since it is important that high priced personnel not be idle waiting for a smoke generator to operate properly), and must mix with the air and stay suspended without changing consistency during the entire filming of a scene. Usually, filming intervals last about one minute, and then will be rerun several times. Accordingly, it is absolutely essential that the smoke maintain a perfect consistency for at least 10-20 minutes. Even prior to filming, it is essential that the f-stop on the camera be set accurately according to the lighting on the filming set. If smoke is to be used on the set, the camera must be set with the smoke in precisely the same color and density as will occur during the actual filming of a scene. The smoke produced during the camera setting session must be precisely reproducible during the filming. While the production of smoke for these purposes may appear to be a simple chore, in actuality it is a very difficult and somewhat artistic science.
Smoke also has many other unobvious uses during filming. For example, when filming period pictures (e.g., Civil War pictures, or other films set prior to the turn of the 20th century), certain background features of the landscape must be obscured for consistency with the time period being portrayed. Thus, antennas, power lines, towers, and even certain buildings must be eliminated from a scene. Normally, this is done by creating a smoke haze which obscures these features from the film. Smoke is also used to create a visible exhaust from cars, puffs from squealing tires, battlefield smoke, and for creation of visible smoke from a burning fire such as a kerosene lantern which would not otherwise be visible on film. The effect of swampy bogs for creature films, and tule fog, is created by producing smoke from a smoke generator and cooling the smoke by passing it through a dry ice chamber; the cooled smoke then settles to produce a heavy fog appearance. Small puffs of smoke may be created through chimney smokestacks or locomotive engines. Even the effect of steam from a stove top cookpot can be precisely controlled by generating a small amount of cooled smoke (as for the generation of tule fog) and placing the smoke on the surface of water in the pot; as the water heats up, the smoke warms and rises and is visible on film in a much more effective way than steam alone.
Accordingly, it is apparent that a smoke-generating machine for special effects has very particular requirements and criteria which must be met. The smoke produced must be white and completely dry, thus enabling it to hang in the air without visible change for 10-20 minutes, and must be non-toxic. The smoke-generating apparatus must be noiseless, and must be capable of generating the dry smoke instantly upon request and in accurately controllable quantities.
Applicant has developed a smoke-generating machine particularly useful for creating special effects and which satisfies all of the foregoing requirements. The machine is portable and consists of a pressurized smoke-generating-liquid holding tank, and a vaporizing chamber having a very high surface area/volume ratio. The vaporizing unit preferably consists of a hollow metal heated block having a vaporizing member loosely mounted within the chamber and configured such that a very narrow path is created for the liquid through the vaporizing chamber. The narrow path, and high surface/volume ratio in the chamber ensure instant and complete vaporization of the smoke-generating liquid. A very small smoke nozzle orifice creates a substantial back pressure in the vaporization chamber, producing a forceful stream of smoke through the nozzle.
Accordingly, it is an object of the present invention to provide a smoke-generating machine which is particularly useful for creating a large variety of special effects for the motion picture, television, and related industries. It is another object of the invention to provide a portable smoke generator which can produce completely dry, white smoke instantly upon demand, and with a minimum amount of noise. These and other purposes are accomplished by the smoke generator of the invention, an embodiment of which is disclosed herein.